Caribbean Clues

First printed in Ellery Queen's Mystery Magazine January 1984, then in 1997 as one of the stories in the anthology The Orion Book of Murder, edited by Peter Haining followed by a story in the anthology Women of Mystery III, edited by Kathleen Halligan.
Selena Mead knows the invitation for a Caribbean Cruise by her husband, Hugh, is just a way to get her help on a Section Q mission. At first he just wanted the cover of being a couple but then it falls to her to help determine if a contact is the real McCoy or a decoy.